Bias potential supply system



April 11, 1939.

P. F G. HOLST BIAS POTENTIAL SUPPLY SYSTEM Filed March 28, 1936 FIXEDDIODE Am BY Q- \INVENTOR Poul FG Hol-st Patented Apr. 11, 1939 UNITEDSTATES BIAS POTENTIAL SUPPLY SYSTEM Poul F. G. Holst, Oaklyn, N. .L,assigfnor to Radio Corporation of America, a corporation of DelawareApplication March 28, 1936, Serial No. 71,361

11 Claims.

The present invention relates to a bias potential supply system forradio receiving apparatus and the like, and has for its object toprovide a bias supply system in connection with a diode signal rectifierfor a radio receiving system, wherein a fixed initial biasing potentialand a signal variable automatic volume control potential may be appliedto certain amplifier tubes.

It is a further object of the present invention to provide a biaspotential supply system for radio receiving systems which provides anautomatic volume control potential and a fixed biasing potential in aconductive supply circuit, and in which a transition from automatic biascontrol to fixed bias control may be accomplished automatically withoutadversely afiecting the operation of the system.

The invention has for its further object to provide an automatic biassupply system responsive to signals which permits a main signalrectifier, diode cathode and controlled amplifier cathodes to beconnected together by a common circuit lead or chassis groundconnection, whereby more stable operation is effected in the radioreceiving system.

The invention will, however, be better understood from the followingdescription, when considered in connection with the accompanyingdrawing, and its scope will be pointed out in the appended claims.

In the drawing,

Figure l is a schematic circuit diagram of a portion of a radioreceiving system embodying the invention.

Fig. 2 is a simplified circuit diagram illustrating the operation of thecircuit of Fig. 1, and

Fig. 3 is a further schematic circuit diagram showing the bias supplycircuit for certain of the other tubes of the receiver and is amodification of the circuit of Fig. 1.

Referring to Fig. 1, a diode type second detector is indicated by theelectric discharge device 5. This device is preferably of the doublediode type, although the two diodes may be inclosed in separateenvelopes. In the present example, however,

the device is an RCA 6H6 tube having two diode rectifiers with separatecathodes, one of which comprises an anode 6, and a cathode 1, and theother of which comprises an anode 8 and a cathode 9, with the seriesconnected cathode heaters indicated at Ill.

The diode rectifier provided by the anode 6 and the cathode I isutilized as a second detector, and is connected with a tuned inputcircuit H provided in connection-with the secondary l2 of anintermediate frequency output transformer 13 to which signals aresupplied from the preceding intermediate frequency amplifier (not shown)through the tuned primary circuit 14.

In series between the tuned input circuit H and the anode 6, there isconnected a suitable filter resistor i5 provided with a by-pass forintermediate frequency currents to the cathode, as indicatedby thecapacitor 16, and a diode output resistor [1, connected in series withthe filter resistor I5, to the cathode lead, indicated at 18. The lattermay be grounded, as indicated at I9, to the chassis or other suitablereturn circuit for the receiving system.

The junction point 2| or negative terminal of the output resistor i! isconnected through a filter resistor 22 with an automatic volume controlsupply lead 23, which leads to the preceding circuits tobe controlled inany well known manner for automatic volume control purposes, and,likewise, the audio frequency component of the rectified signalappearing in the output resistor ll may be taken therefrom for furtheramplification in any well known manner through an output lead 24. Thebias supply or automatic volume control circuit 23 is suitably by-passedto ground at high and audio frequencies by the bypass capacitor 20.

In order to establish a fixed biasing potential on the automatic volumecontrol circuit and on the tubes controlled thereby, in the absence ofsignals, a fixed source of biasing potential is provided in connectionwith a fixed potential source represented by the bleeder resistor 25 ofthe receiving system and the remaining diode rectifier provided by theelectrodes 8 and 9. For this purpose, the cathode 9 is connected to amore negative potential tap-point 26 on the source 25 than theconnection for the anode 8, which is provided through a lead 21, theresistor 22, the output resistor H, and a lead 28, connected with a morepositive tap-point 29.

With the arrangement shown, and with a negative potential ofsubstantially three volts between the points 26 and 29, a current iscaused to flow thereby from the positive terminal 29 through theresistors I1 and 22 andthe lead 21 to the anode 8 from which the currentflows from the cathode 9 and returns to the negative terminal 26. Thecathode I and the positive end of theresistor H are grounded, and,therefore, because of the direction of current fiow in the resistors apotential proportional to the relative values of the-resistors l1 and 22is placed upon the diode anode B, the audio frequency lead 24 n and theautomatic volume control lead 23 with respect to ground, this being ineach case of a lesser value than the bias potential difference betweenthe terminals 29 and 26, and is suflicient to maintain the circuit 23 ata predetermined desired negative potential with respect to ground or thecommon cathode circuit for the receiving system.

As signals are received, the current through the main diode or detectoroutput resistor I1 is caused to increase because of rectification of thecarrier wave or signal and this tends to raise the potential in anegative direction at the terminal 2i and at the anode 8 through itsconnection therewith until the potential of the anode 8 equals thepotential of the cathode 9, when no further current now takes placethrough the control diode 8-9 since the cathode and anode are of thesame negative potential. The automatic volume control circuit then takesover the control and the potential applied to the circuit leads 23 and24 is proportional to the strength of the carrier wave or signal andserves to properly bias the circuits in the usual manner to effeet theusual automatic volume control of the preceding portion of the receiver.

The manner in which the system operates to control the precedingamplifier tubes of the receiver is shown more clearly in Fig. 2 to whichattention is now directed and in which the same reference numerals areapplied to like circuit elements, as in Fig. 1.

As will be seen in Fig. 2, the intermediate frequency amplifier tubesindicated at 39, are provided with a control grid 3i and a cathode 32,connected respectively with the automatic volume control lead 23 and thecommon circuit return or ground l9, and in a similar manner the radiofrequency amplifier tubes, represented by the tube are provided with acontrol grid 34 and. a

I cathode 35 connected in a similar manner for automatic volume controlbetween the lead 23 and ground l9.

The fixed source of biasing potential between the terminals 26 and 29 isapplied between the round i9 and the cathode 9, and the anode 8 isconnected with the lead 23, whereby current is caused to How through theconnection with the output resistor IT and the series filter resistor22, which potential drop through both elements is applied between thegrids and cathodes of the amplifier tubes 30 and 33. This initial biasis determined by the value of the potential between the terminals 26 and29 and it will be noted that the polarity is such that the fiow ofcurrent through the diode output resistor is in the same direction aswhen a variable potential resulting from signal rectification is derivedbetween ground !9 and the terminal 2| and applied through the resistorH, the drop and potential being transferred through the output filterresistor 22 to the automatic volume control lead 23.

From the diagrammatic representation, it will be seen that when theterminal 2| becomes as negative as the terminal 26, both the anode 8 andthe cathode 9 will be at the same negative potential and furtheroperation of the rectifier will be discontinued. The control of thetubes 30 and 33 representing any of the preceding amplifier tubes of thereceiver will then be entirely under control of the variable source orrectified signal potential.

Viewed in one of its aspects, the rectifier device 8-9 is a check-valvepreventing the fiow of current through the fixed source from theautomatic volume control circuit when the latter provides a higher thana predetermined potential. In other words, the controlling diode 8-9serves to disconnect the fixed source of biasing potential as soon asthe variable source or automatic volume control means reaches apredetermined value. Furthermore, use is made of both the filterresistor and the diode output resistor for providing the initial biasingpotential while for automatic volume control operation, the filterresistor functions only as a filter.

The relative resistance values of the filter resister and the diodeoutput resistor in series determines the relative amount of delaypotential or negative bias which is applied to the detector diode anode6. In the present example, where the resistor ll may have a value of220,000 ohms, for example, and the resistor 22 may have a resistance of2.2 megohms, the negative biasing potential on the diode anode 6 may beof the order of less than .3 volt, thus causing no appreciable delay inthe response to signals, the major portion of the drop in potentialbeing through the series resistor 22.

Referring to Fig. 3, a rectifier device 40 is arranged to provide,through a filter 4|, rectified alternating current at positive andnegative output terminals 63 and 44, respectively, from a usualalternating current step-up transformer 45.

Without the use of the usual bleeder or output resistor, theanode-cathode space paths of the audio frequency amplifier tubes,represented by the tubes 45-46 are parallel connected in series with aresistor 4'! in the negative supply lead, and the circuit return theretois made through ground or common circuit return connections 48. Thisavoids the shunt load of the usual output resistor, While at the sametime providing fixed biasing potentials in connection with the resistor41 to which the control grids 48 and 49 may be returned through suitablecircuits represented by the connections 50. The coupling elements havebeen omitted for the sake of simplifying the drawing and. permitting thecircuits to be traced more readily. The control diode comprising theelectrodes 9 and 8 are connected as in the preceding figures with thediode output resistor l1 and the series resistor 22 between the groundand a negative tap for example, on the resistor 41.

It will be seen from a consideration of Figs. 2 and 3, that the highfrequency and low frequency amplifier tubes are separately biased bydifferent means and that by the system of Fig. 3 the voltage dividerresistor 25 may be omitted, while at the same time the control diode ispermitted to operate in connection with the detector diode to provide aninitial bias potential across both the series resistor and the diodeoutput resistor with the. same polarity to ground as the diode, whenoperating to supply a potential across the diode output resistor andthat this connection serves to raise the diode anode negatively to avalue equal to the cathode to reduce its operation to zero. As in thecase of the radio frequency and intermediate irequency amplifier tubes,the audio frequency amplifier tubes are by this means also permitted tohave the cathodes 52 thereof connected directly to the common returncircuit or ground.

I claim as my invention:

1. A bias control system for radio receiving apparatus and the likehaving a common cathode return circuit, comprising in combination adiode rectifier, means providing a source of fixed poten- Iii tial,means providing a source of variable potential, and means for causingsaid last named potential to vary in response to signal strengthvariations, said potential sources having positive terminals directlyconnected with said common cathode return circuit for said apparatus andhaving negative terminals interconnected through said diode rectifier.

,2. A bias control system for radio receiving apparatus and the likehaving a common cathode return circuit, comprising in combination adiode rectifier, means providing a source of fixed potential, meansproviding a source of variable potential, means for controlling thevalue of the last named potential in response to signal strengthvariations, said potential sources having positive terminals directlyconnected with said common cathode return circuit for said apparatus andhaving negative terminals interconnected through said diode rectifier,and the cathode of said rectiher being connected with the negativeterminal of the fixed source and the anode being connected with thenegative terminal of the variable source through a series filterresistor.

3. A bias control system for radio receiving apparatus and the likehaving a common cathode return circuit, comprising in combination adiode rectifier, means providing a source of fixed potential, meansproviding a source of variable potential, means for controlling thevalue of the last named potential in response to signal strengthvariations, said potential sources having positive terminals directlyconnected with said common cathode return circuit for said apparatus andhaving negative terminals interconnected through said diode rectifier,the cathode of said rectifier being connected with the negative terminalof the fixed source and the anode being connected with the negativeterminal of the variable source through a series filter resistor, a biascontrol circuit connected with said anode, and an output resistor forthe variable source connected between said common circuit connection andthe negative terminal of said variable source.

4. In a bias potential supply system for amplifying apparatus embodyinga plurality of electric discharge amplifier devices, the combination ofa diode rectifier device, means providing a common cathode returncircuit for said amplifier devices to which the cathodes of said devicesare directly connected, a bias potential supply lead for said amplifierdevices, means providing a fixed biasing potential for said amplifierdevices having a negative terminal and having a positive terminalconnected with said supply lead through said diode rectifier device, theanode electrode of said rectifier device being connected with saidnegative terminal, means including a rectifier output resistor providinga potential proportional to the strength of a received signal, said lastnamed means having a positive terminal provided with a direct connectionwith said common return circuit and a negative terminal connected withthe anode of said rectifier device, a filter resistor in circuit withand having a relatively higher resistance than said last named means.

5. In a radio receiving system, the combination with a second detectorcomprising a diode thereof with respect to the cathode end, meansadapted to provide a fixed biasing potential, a control diode rectifierdevice having an anode connected with said last named lead and having acathode connected to the cathode of the first named rectifier throughsaid source of fixed biasing potential, the positive terminal of whichis connected with the cathode of the first named diode rectifier and thenegative terminal of which is connected with the cathode of the controldiode rectifier.

6. In a bias potential supply system for radio receiving apparatus andthe like, including in combination a plurality of amplifier tubes, thecathodes of which are connected with a common circuit return element,means providing a source of biasing potential having a positive terminalconnected with said common circuit return element, means providing abias potential supply connection for certain of the amplifier tubesdirectly with said last named means, means providing a bias potentialsupply connection for certain others of said amplifier tubes with saidbias potential source including a diode rectifier device in saidconnection, means providing a conductive resistance path between theanode of said device and the common circuit return element, and meansproviding automatic volume control potentials in connection with aportion of said resistance path and of a polarity such that the 1positive terminal thereof is connected with the common circuit returnelement.

7. The combination with a direct current bias potential supply circuitfor radio receiving systems and the like, of a diode rectifier device insaid circuit having a cathode and an anode, means for maintaining saidcathode at a negative potential with respect to the cathode returncircuit of said system, a negative bias supply circuit connected withsaid anode, and means for raising the negative potential on said anodewith respect to the negative potential on the cathode in response to anincrease in signal strength, said last named means having a positiveterminal connected with the cathode return circuit of said system by adirect connection.

8. In a radio receiving system, having a plurality of high frequency andlow frequency amplifier tubes, the combination of means providing acommon cathode circuit connection therefor through said system,potential supply means having a positive terminal connected with saidcommon cathode circuit connection, a signal rectifier device including acathode and an anode, a diode output resistor therefor having aconnection with the anode, the, cathode of the rectifier device beingdirectly connected with said common circuit connection and directly withsaid diode output resistor, a bias control circuit for the highfrequency amplifier tubes connected to the negative terminal of saidoutput resistor, a filter resistor in series therewith, having arelatively high resistance with respect to said diode output resistor,and an auxiliary diode rectifier device having a cathode connected witha negative terminal of said potential supply means and having an anodeconnected with said bias control circuit whereby it is connected inseries with said diode output resistor and filter resistor in series,whereby the potential of the signal rectifier device cathode is not lessthan the potential of the controlled amplifier cathodes.

9. In a radio receiving system, the combination with a plurality of highfrequency amplifiers having the cathodes thereof connected to ground,

of a diode signal detector having a cathode connected to ground, a diodeoutput resistor connected with said detector to receive the rectifiedsignal output therefrom and having the positive end connected to ground,a series filter resistor through which automatic volume controlpotentials are supplied from said diode output resistor to the controlgrids of said high frequency amplifiers, means providing an auxiliarydiode rectifier, means for raising the cathode thereof above ground by apredetermined negative potential, means for applying said automaticvolume control potentials to the rectifier anode to raise said anode toa higher negative potential than the rectifier cathode in response toreceived signals and providing a connection whereby the potential of thedetector diode cathode is not less negative than the potential of thecontrolled amplifier cathodes.

10. A bias control system for radio receiving apparatus and the likeincluding a common cathode return circuit, comprising in combination adiode rectifier, means providing a source of fixed potential, meansproviding a source of variable potential, means for causing said lastnamed potential to vary in response to signal strength variations, saidpotential sources having positive terminals directly connected with saidcommon cathode return circuit for said apparatus and having negativeterminals interconnected through said diode rectifier, and a circuit forderiving a biasing potential therefrom, connected with said dioderectifier and said cathode return circuit.

11. In a radio receiving system, the combination with an amplifier gaincontrol circuit comprising a common cathode return circuit element and abias supply lead normally negative with respect thereto, of a diodesignal rectifier having an output resistor connected in circuittherewith to receive the rectified signal output therefrom, said outputresistor having a positive terminal connected directly to the commoncathode return circuit element, a filter resistor connected between anegative terminal of said output resistor and said negative bias supplylead, and a direct current residual bias supply circuit connectedbetween said negative bias supply lead and the common cathode returncircuit element, said last named circuit including a second dioderectifier device having an anode electrode connected with said negativebias supply lead, and having a cathode, and said circuit furtherincluding means providing substantially fixed biasing potential inseries with said second diode rectifier device, the negative terminal ofsaid last named biasing means being connected with the cathode of thesecond diode rectifier device, and said last named bias means having apositive terminal connected to said common cathode return circuitelement.

POUL F. G. HOLST.

